1. Field of the Invention
The present invention relates to a sensor system that allows measuring and monitoring of angular position in two or three axes. The sensor system of the present invention references its position according to the Earth's magnetic field or a magnetic field provided by the user. Accordingly, the sensors of the present invention are useful for a variety of purposes, including, virtually any application that requires monitoring and measurement of any combination of roll, pitch, and yaw.
2. Description of the Prior Art
There are a variety of sensors known in the art for use in measuring magnetic fields, such as Hall effect sensors, proton quantum interference detectors (SQUID), fluxgate magnetometers, inductive pickup sensors, magnetoresistive sensors, and others. Depending upon the application, one or another of the above sensors may be chosen for a particular magnetic field measurement.
Magnetic field sensors provide a highly effective means of measuring both linear and angular displacement. This is because even quite small movements of actuating components in machinery, for example, metal rods, gears, cams, etc., can create measurable changes in magnetic field.
The art was previously dominated by Hall effect sensors that make use of the property of a current-carrying semiconductor membrane (Hall element) of generating a low voltage perpendicular to the direction of current flow when subjected to a magnetic field normal to its surface. More recently, magnetoresistive sensors have proven to be very versatile as replacements for Hall effect sensors in magnetic field measurement.
Magnetoresistive sensors make use of a magnetoresistive effect which is a property of a current-carrying magnetic material to change its resistivity in the presence of an external magnetic field. This change is brought about by rotation of the magnetization relative to the current direction. A typical magnetoresistive sensor comprises a polarized element within a flux collector that exhibits a change in resistance in the presence of a magnetic flux. The polarized element may be linear or it may be arranged in geometric patterns, such as meandering the element through the flux collector. Through arranging the element nonlinearly within the flux collector, one is able to increase the length of the element while maintaining a small size of the overall sensor. Further, the resistance of the element increases as length increases and since the sensor operates by changes in resistance in the element, overall sensitivity of the sensor is enhanced. An overview of many of the attributes and functions of magnetoresistive sensors are found in "The Magnetoresistive Sensor" Technical Publication No. 268, a product brochure of Philips Components.
In many applications, it has been believed that in order to measure angular positioning in three axes it is necessary to utilize at least three sensors to provide three outputs which may be compared to determine the change in angular positioning. It will be also appreciated that electronic compasses, for example, have been developed with just one or two sensors. However, compasses only need to measure in a single axis.
Prior art sensor systems which have been developed for use in monitoring in three axes have required somewhat complex electronics and have also been of high price. Thus, a need remains in the sensor art for a sensor system that may measure angular positioning in three axes without being burdened by complexity.